This disclosure relates to a developing device that forms a toner image by feeding toner toward an electrostatic latent image formed on a circumferential surface of a photosensitive drum by electrophotography and an image forming apparatus having the same, and particularly to a technique for preventing leakage of toner on a circumferential surface of a developing sleeve.
In such an electrophotographic image forming apparatus, a toner image is formed by feeding toner from a developing device toward an electrostatic latent image formed on a surface of a photosensitive drum. Such a developing device has a developing roller made up of a magnet roller and a developing sleeve, forms a toner layer on a circumferential surface of the developing sleeve, and feeds toner from the developing sleeve to the surface of the photosensitive drum.
In such a developing device, a seal member made of a magnet is used as a member for preventing the toner on the circumferential surface of the developing sleeve from leaking out of a developing region. The seal member prevents the toner from leaking out of the developing region by causing a concentrated magnetic field to be formed at magnetic poles of the magnet roller and edges (corners) of the seal member by a magnetic field emitted from the magnet roller that is disposed at a fixed distance from the developing sleeve and is encased in the developing sleeve, and by forming a magnetic brush depending on the toner. During the rotation of the circumferential surface of the developing sleeve, a part of the toner which is present within a sealing region caused by the seal member may remain attached to a surface of the developing sleeve, and a toner layer may be formed on the developing sleeve. However, such a toner layer is recovered from the circumferential surface of the developing sleeve along with the rotation of the developing sleeve by a tip of the seal member (which is a seal member portion located furthest upstream in a rotational direction of the circumferential surface of the developing sleeve, and is called a jaw part). However, the collected toner gradually accumulates at the tip by repetition of the developing operation, and eventually falls outside a developing unit, causing leakage of the toner.
For this reason, there is a proposal for a developing device A for preventing the toner from accumulating on the tip of the seal member by providing a developer scraping member in the vicinity of a gap portion between the developing sleeve and the magnetic seal and coming into contact with the developing sleeve to thereby scrape up a developer.
Further, there is also a proposal for a developing device B for preventing the developer from accumulating on the tip of the seal member by forming a taper at the tip of the seal member.